1. Field of the Invention
The present invention relates to processes for producing a substrate with a piercing aperture, a substrate for a liquid ejection head and a liquid ejection head.
2. Description of the Related Art
As methods for forming a liquid supply port in an element substrate of a liquid ejection head, methods such as drilling, laser beam machining and sand blasting, and anisotropic crystal etching have been proposed.
In a method of forming a liquid supply port by dry etching using an etchant gas, a liquid supply port of an almost perpendicular form is formed. As a result, a chip size can be made smaller than a case where a liquid supply port is formed by anisotropic crystal etching.
In the method of forming the liquid supply port by the dry etching, an etch-stop layer is formed on a front surface of an element substrate. Dry etching is then performed from a back surface of the element substrate to the etch-stop layer to form a piercing aperture. Thereafter, the etch-stop layer is removed.
Here, it is known that when an etched surface reaches the etch-stop layer, a phenomenon called notching in which the etching proceeds to a direction perpendicularly to a supply port forming direction (hereinafter also referred to as a lateral direction or plane direction) by influence of charging occurs. When the notching occurs, an opening portion of the liquid supply port on the front surface of the substrate is spread, in some cases, up to a heat-generating element or a wiring thereof, thereby lowering reliability.
Japanese Patent No. 4119379 describes a process of forming a first trench in a front surface of a substrate and forming a second trench in a bottom portion of the first trench from a back surface of the substrate. According to this process, it is said that influence of notching is not exerted upon the formation of the second trench because an end portion of a liquid supply port is defined by the first trench.